Suspension bridge

ABSTRACT

A suspension bridge comprises at least two Y-shaped towers between which are suspended a plurality of catenary cables. These cables are formed into a mesh or lattice by transverse connecting cables which hang down on either side and are attached to the edge of the bridge deck. Thus the bridge is formed of a plurality of closed cells having the shape of convex polygons whose upper corners are defined by the catenaries and whose lower side is the deck. The cable net is prestressed (pretensioned) against the deck or load (pipeline) and against the anchor blocks provided at the ends of the catenary cables.

United States Patent [191 Sofronie Dec. 31, 1974 SUSPENSION BRIDGE [75] Inventor: Ramiro Sofronie, Bucharest,

Rumania [22] Filed: Apr. 10, 1972 [21] Appl. No.: 242,357

447,247 3/1968 Switzerland 14/18 738,644 8/1943 Germany 14/18 569,735 2/1933 Gennany 14/18 Primary Examiner-Nile C. Byers, Jr. Attorney, Agent, or Firm-Karl F. Ross; Herbert Dubno [57] ABSTRACT A suspension bridge comprises at least two Y-shaped towers between which are suspended a plurality of down on either side and are attached to the edge of (g1. catenary cablw These cables are formed into a mesh [58] Field of Search 14/19, 2O 21 22, or lattice by transverse connecting cables WhlCh hang 14/23 1 the bridge deck. Thus the bridge is formed of a plurality of closed cells having the shape of convex polygons [56] References Cited whose upper corners are defined by the catenaries and UNITED STATES PATENTS whose lower side is the deck. The cable net is pre' 718,237 l/1903 Zimmerman 14/19 X stressed (pretensioned) against the deck or load (pipe- 2, 8 2/ 5 enan line) and against the anchor blocks provided at the 3,055,484 9/1962 Hubert 14/ 18 X ends of the catenary 1 FOREIGN PATENTS OR APPLICATIONS 2 Claims 8 Drawing Figures 1,186,682 2/1959 France 14/18 n a! A Tal w Pmimenvm 3.857.130

SHEETIOF 2 FIG. 1

FIG]

SHEET 2 BF 2 FIG. 8

FIG. 5

FIG.3.

FIG. 5

FIG.7

SUSPENSION BRIDGE FIELD OF THE INVENTION The present invention relates to a suspension bridge and to a method of making same. More particularly this invention concerns an arrangement for suspending an elongated load, such as a vehicular or personnel deck, utility pipeline or electrical cable.

BACKGROUND OF THE INVENTION There are generally three conventional types of suspension bridge: U-section wherein the deck or load forms the root of the U and the cables the arms, inverted T wherein the deck forms the lower crosspiece and the cables the vertical leg, and triangle or A (delta) wherein the deck is the lower side and the cables or suspension elements form the other two sides and originate from a common location. In all three arrangements the decks take over the flexing and twisting forces in the bridge while the cables define the funicular polygons of the vertical load. Three other types of suspension bridge are known: L-shaped, inverted Y, and V in which the cables assume both the vertical and horizontal loads.

In all of the six above-mentioned types the bridges offer little torsional resistance to lateral forces as generated, for example, by the wind. For this reason these bridges must be reinforced in any of three major ways. In one arrangement the desks are made as truss girders, or statically stiff closed or boxed frames. In another arrangement one reduces air drag by designing the bridge as openly as possible and providing it with aerodynamically shaped balustrades and the like. Finally a secondary network of cables may be provided to supplement the hangers, this secondary network lying at an inclination to or in a plane different from the hanger cables.

These methods of increasing bridge stability are all of limited efficacy. In addition they are expensive to realize because they are designed based on wind-tunnel tests, and equally complicated skills and techniques are required to fabricate such bridges. More common disadvantages are the considerable mass of such static structures, the higher fabrication costs and the overdimensioning necessary to accommodate the added mass.

OBJECTS OF THE INVENTION It is therefore an object of the present invention to provide an improved bridge structure which obviates the aforementioned disadvantages.

Another object is the provision of an improved suspension bridge which has great torsional resistance.

Yet another object is to provide such a bridge which is of simple and inexpensive construction.

It is also an object of the invention to provide an improved method of making such a suspension bridge.

SUMMARY OF THE INVENTION I attain these objects with a bridge that is, seen in cross section, closed, and, seen in longitudinal vertical section, symmetrical. Such a structure is effectively prestressed in three mutually orthogonal directions, that is transversely and longitudinally in the horizontal plane and vertically. More particularly the bridge according to the present invention comprises a pair of towers between which are spanned at least two catenaries each connected via upright hangers to the elongated load or bridge deck. The catenaries are connected directly together by means oftransverse elements, advantageously cables, so that in cross section the bridge structure is a funicular polygon of the forces in the bridge. More particularly, the transverse cables lie along funiculars of the transverse loading of the longitudinal cables or catenaries.

According to another feature of the invention an array of catenaries is used, with the transverse connecting cables connected to all of the catenaries which do not run exactly parallel to each other, the' outer ones being bowed horizontally inwardly. This forms a lattice or mesh that has great resistance to lateral and torsional forces. Thus the catenaries which are horizontally equispaced define a longitudinally upwardly and transversely downwardly concave surface. The hangers can be unitary with the transverse cables, so that each hanger extends up from one side of the deck and over the catenaries, then down on the other side of the bridge where it is connected to the other side of the deck.

According to another feature of the invention Y- shaped towers are provided whose Y-arms are interconnected by an arch to which the catenaries are attached or on which they rest. The deck is received in the crotch of the Y. The catenaries are generally spanned over the arch and either form another span or are anchored to the ground either through the intermediary of an anchor yoke straddling the deck or by means of simple anchor blocks to either side of the deck. Such a bridge can be used for supporting a roadway, a railway, a canal, or electrical or water-supply lines.

It is of course necessary to suspend the outer catenaries first. Thereafter the hangers and deck can be put in and the inner catenaries, if any, may be hung, closing the operation with the fixing of the transverse connecting cables that form a mesh with the catenaries. Alternatively it is possible to make the supporting catenary net first, and thereafter hang the deck on the hangers.

According to an important feature of the invention, the suspension bridge is formed from at least two longitudinally spaced towers of generally Y-configuration with the portion above the crotch of the Y having the shape of a del (inverted delta), the upper limb of which is of upwardly convex curvature.

The catenaries, at least three in number, so as to define a donwardly concave or upwardly convex curve in cross-section, rest upon the upper limb of the del under a pretension which exceeds that generated by the weight of the deck in the absence of vehicular traffic. As used herein, the term deck refers to the less flexible span portion of the bridge interconnecting the tube towers and anchored at its ends under tension while forming, in the case of a bridge, the walkways, vehicular roadways and like portions of the bridge, carrying traffic. The term is used, moreover, to refer to any upwardly bowed tensioned body lying in the crotches of the towers, whether constituting a pipeline for the delivery of fluids, electrical cables or combinations thereof, and combinations of such utility deck with bridge decks.

The elongated deck is held by the cable net under tension even in the absence of wind or traffic. The hanger cables, which are integral with the transverse cables of the net in each vertical, or substantially vertical plane, are inwardly and downwardly inclined while being under a permanent prestress (pretension) beyond that generated by the weight of the deck and even in the absence of wind or traffic. Since the transverse cables are integral with (unitary or in one piece with) the hanger cables, they describe an upwardly convex curvature. Hence, the longitudinal cable or catenaries and the transverse cables are mutually orthogonal and of opposite curvature.

The towers, according to the invention, have columns which are seated on the ground in the usual foundations and have the arms of the Y spanned by rigid members forming the upper limb of the del mentioned earlier. As a result, the net formed by the cables, constitutes with the deck a prestressed polygonal tube at least the upper limb of which is curved and which has elastic stability. The prestress or pretension is capable of withstanding short-term or instantaneous lateral loading (from wind or the like) without fluttering and shortor long-term overloading of the deck. Furthermore, short-term influences such as those of earthquakes can be withstood without difficulty.

DESCRIPTION OF THE DRAWING The above and other objects, features, and advantages will become apparent from the following, reference being made to the accompanying drawing in which:

FIG. 1 is a side elevational view ofa bridge according to the present invention;

FIG. 2 is a top view of the bridge of FIG. 1;

FIG. 3 is a cross section through the bridge;

FIG. 4 is a perspective view ofa portion of the bridge;

FIG. 5 is a longitudinal section through the portion of the bridge shown in FIG. 4;

FIG. 6 is a cross section through the bridge adjacent the support tower;

FIG. 7 is a section taken along line VII-VII of FIG. 6; and

FIG. 8 is an alternative embodiment of the invention, in a view corresponding generally to FIG. 6.

SPECIFIC DESCRIPTION As seen in the drawing a pair of support towers or pylons 8 carry a catenary net or cable sheet 1, 2, 3 formed of central catenaries 1, outer catenaries 3, and transverse connecting cables 2. As in a net, each transverse cable 2 is connected to the catenary cables 1, 3 at each junction, eg by a conventional cable clamp. It can be seen in FIG. 3 that the cables 2 define generally funicular polygons along with hangers 4 which are simply the end portions of the cables 2. The cables 1, 2, and 3 intersect at joints and are interconnected at their junctions where in any case of strain they transmit force one to the other, each being curved in the opposite direction to the other. Each cable 2, 4 has one end connected to one edge ofa deck 5, extends up and over the catenaries l and 3, and then has its other end connected to the other longitudinal edge of the deck 5, which can be of any conventional type, such as'described in US. Pat. No. 3,132,363. Each facing pair of hangers 4 lies in a vertical plane P, but can also lie in planes inclined to the vertical, such as indicated at P in FIG. 5.

Each tower 8 is generally Y-shaped, with a pair of Y- arms 80 and 8b and a central support foot or stem 80 resting on the ground. The deck 5 is supported by a cushion 9 at the crotch of the Y-support or tower 8. In addition the upper ends of the two arms 8a and 8b are unitary with and interconnected by an upwardly convex arch 6 which is provided with supports 7 for the cables l and 3.

FIGS. 1 and 2 show how at one end the cables are secured to a yoke 10 which is anchored to the ground at 11 and straddles the deck 5 where it runsinto the ground. At this end the system of transverse cables 2 and hangers 4 is provided right up to the anchors 11 to support the roadway 5. On the opposite side the roadway 5 is supported by piers or pillars l3 and the catenaries or cables 1 and 3, not interconnected by webforming transverse cables 2, are drawn to each side of the deck 5 and secured to anchor blocks 12.

FIG. 8 shows the two arms 8a and 8b can be joined at their top ends by a straight element 6 when no inner catenaries are used, the bridge being suspended only from the outer lines 3. In this case the interconnecting cables 2 are always straight and the overall closed form of the bridge in section is retained for best torsional and lateral stability, with the bridge being several times wider at its top than at deck 5, thereby having the shape of an inverted A or delta like the upper portion of the towers 8.

The suspension bridge according to the present invention is effectively formed of a plurality of closed cells having the shape of convex polygons whose upper corners are defined by the catenaries 1 and 3 and whose lower side is the deck 5. This makes for prestressing that ensures support of the deck by the cable net no matter in which direction it is loaded. The me chanical stability, i.e. the stability of static deflections and free oscillations caused by permanent and service loads, wind gusts or earthquakes, is ensured by the intrinsic parameters of the structure. The aeroelastic stability, i.e. the stability of static deflections, forced oscillations and self-excited oscillations caused by the interaction of the elastic, dissipative and inertial forces with the aerodynamic forces is ensured by the critical speeds of the bridge. In addition such a bridge can be made in an extremely open and light way so that a minimum of expensive materials need be employed, since the closed structure prestresses the bridge in every direction and no extra structural elements need be provided just to make the bridge rigid: all of the bridge structure serves to support the deck. The term prestress is used herein to indicate that a pretension is provided in the absence of the supported load such that application of the load will at least partly compensate for the prestress. Thus the method of the present invention comprises the steps of erecting at least two towers having upwardly diverging arms and of a Y configuration, the arms being spanned by a curve upwardly convex limb. A cable net is suspended from the limb and comprises at least three transversely spaced catenaries of upwardly concave curvature supported on the limbs and a multiplicity of transverse cables extending across, attached to said catenaries and of upwardly convex curvature. A deck is suspended from the ends of the transverse cables and is retained within the crotches of the towers formed by the arms. The cables are tensioned against each other and the deck and maintain the deck under tension even in the absence of loading. The deck is supported on the towers by threading the catenaries beneath the transverse cables after the same have been attached to the deck.

I claim:

1. A suspension bridge comprising:

a pair of upright support towers;

at least three horizontallyspaced catenary cables spanned longitudinally between said towers;

a plurality of connecting cables extending transversely between said catenary cables and connected thereto at mutal junctions, said cables defining a cable net of longitudinally upwardly concave and transversely downwardly concave curvature;

a plurality of hangers formed by extensions of the connecting cables and depending from the outermost two of said catenary cables; and

an elongated load suspended from said hangers below said net, said towers being Y-shaped with upwardly diverging arms, said load being received in the crotches between the Y-arms of said towers, said cable net being supported by said arms, each tower having a downwardly concave upwardly convex arch spanning its arms, said catenary cables resting on said arch and being provided at their ends with means anchoring them to the ground, said outermost catenary cables being spaced apart by a transverse width severaltimes greater than the transverse width of said load, said cables being under tension against each other and against said load whereby said net is under stress.

2. A suspension bridge comprising:

a pair of upright towers;

at least three horizontally spaced catenary cables spanned longitudinally between said towers;

a plurality of transverse cables transversely spanning said catenary cables and each lying generally in the configuration of an inverted delta and each having a pair of end hanger portions each depending from a respective outer one of said catenary cables and a central connecting portion extending transversely across said catenary cables and connected to each of them at intersecting junctions of the catenary and transverse cables, said connecting portions and said catenary cables defining a cable net, said cables being under tension against each other, whereby said net is under stress,

an elongated load suspended from said hanger portions below said net, the ends of the catenary cables being secured to yokes which are anchored to the ground, each of said towers having a portion shaped as an inverted delta with a pair of downwardly convergent rectilinear legs and an upwardly convex curved base, said base carrying said net.

* l= l= I 

1. A suspension bridge comprising: a pair of upright support towers; at least three horizontally spaced catenary cables spanned longitudinally between said towers; a plurality of connecting cables extending transversely between said catenary cables and connected thereto at mutal junctions, said cables defining a cable net of longitudinally upwardly concave and transversely downwardly concave curvature; a plurality of hangers formed by extensions of the connecting cables and depending from the outermost two of said catenary cables; and an elongated load suspended from said hangers below said net, said towers being Y-shaped with upwardly diverging arms, said load being received in the crotches between the Y-arms of said towers, said cable net being supported by said arms, each tower having a downwardly concave upwardly convex arch spanning its arms, said catenary cables resting on said arch and being provided at their ends with means anchoring them to the ground, said outermost catenary cables being spaced apart by a transverse width several times greater than the transverse width of said load, said cables being under tension against each other and against said load whereby said net is under stress.
 2. A suspension bridge comprising: a pair of upright towers; at least three horizontally spaced catenary cables spanned longitudinally between Said towers; a plurality of transverse cables transversely spanning said catenary cables and each lying generally in the configuration of an inverted delta and each having a pair of end hanger portions each depending from a respective outer one of said catenary cables and a central connecting portion extending transversely across said catenary cables and connected to each of them at intersecting junctions of the catenary and transverse cables, said connecting portions and said catenary cables defining a cable net, said cables being under tension against each other, whereby said net is under stress, an elongated load suspended from said hanger portions below said net, the ends of the catenary cables being secured to yokes which are anchored to the ground, each of said towers having a portion shaped as an inverted delta with a pair of downwardly convergent rectilinear legs and an upwardly convex curved base, said base carrying said net. 